Recent studies have documented the presence of high concentrations of insulin specific insulin receptors, and direct metabolic effects of insulin in the brain. Thus the possibility of direct participation by insulin in brain function, growth, or development can be studied. We propose to establish a functional role for insulin receptors in the rat brain, to study the hormonal specificity of these receptors, and to determine factors which regulate these receptors in the normal animal and in animals with disorders of carbohydrate metabolism. The proposed research will be in four parts. First, we will measure the binding of insulin and its metabolic effects (macromolecular biosynthesis) on the rat brain from fetal life through the postnatal period of rapid brain growth and in adult animals. This will be done using plasma membranes prepared from the brain and using neurons and glia in separate tissue cultures. Second, we will determine the specificity of these receptors using a variety of insulins from different species, insulin analogs, and growth factors which are structurally related to insulin. Third, we will study the in vitro effects of excessive glucose and insulin and the effects of pathological conditions in rodents (viz, fasting, obesity, insulin-dependent diabetes mellitus) on the concentration and affinity of insulin receptors in the brain. Fourth, we will determine the location of insulin and insulin receptors in subcellular fractions of the neuron to assess insulin's role in neuro-transmission. This will be done in subcellular fractions prepared from neurons obtained from fresh brain and with neurons in culture. These studies will extend the knowledge of role of insulin in the brain as a possible growth-promoting hormone and/or neurotransmitter or neuromodulator and elucidate factors which may be important in understanding the pathophysiology of infants of diabetic mothers, obesity, and insulin-dependent diabetes mellitus.